If you're familiar with the term "Cock Block," you know that it means one dude messed up another dude's game with the ladies. Well, this happens to girls too. And we (most of us) don't have cocks.

If you've ever been obviously checking out a guy and then your friend decides to "claim" him by walking up to him and touching his polo shirt and exclaiming, "I'm soooo drunk right now omg!"- you've been clam jammed.

If you've ever been hitting it off with a guy and then you tell him his pong game is weak, you've been clam jammed.. by yourself, I might add.

(noun)the female equivalent of a Cock-Block; a person who interferes with a woman's chance of getting laid, lucky, or boned; generally the "ugly friend" or "previously rejected."
(verb) to block a female from getting sex.
also Clam-Jammy (adj) describing a person with nookie blocking qualities, who may pose a threat to other men-seeking women.

"Jane, you are a bitter Clam-Jam! That guy was incredibly hot, and now he's gone!"
"That Clam-Jam may be five-foot-ten, but I have the Kama Sutra memorized and he'll never know."
"I am going to Clam-Jam Samantha, because that nasty wench spilled my drink and flirted with my boyfriend."
"There is a very Clam-Jammy cougar leaning at the bar, and I'd like to cut off her stilettos with a nail file."